1. Field of the Invention
The present invention relates to a battery charging method, and more particularly, to a battery charging method that modifies a charge-off voltage up or down, thereby extending battery service life.
2. Description of Related Art
Because of characteristics associated with the materials of Lithium cells, the Lithium cells generally may not be charged at voltages over 4.2 volts; otherwise the service life of the Lithium cells may be shortened significantly or otherwise compromised. When the Lithium cells are charged at voltage levels that are much higher than 4.2 volts, the lithium cells may be in danger of burning or even blowing up.
Please refer to FIG. 1, in which a curve of a conventional lithium battery in charging is demonstrated. Initially, the lithium cells are charged by applying a constant current (see curve I), and then later charged by a constant voltage (curve V). In the initial constant current charging stage, the battery voltage continuously increases up to a predetermined charge-off voltage Voff, which is the voltage at which the charging is switched off. While the battery voltage reaches the charge-off voltage Voff, the battery charging enters the constant voltage charging stage. When lithium cells are charged in a constant voltage charging stage, the charging current gradually decreases. As the battery current reaches a predetermined charge-off current Ioff, the point at which the current charging phase is ended, the lithium cells are fully charged.
Additionally, another method of conventional battery charging applies on/off switches to modulate charging currents for lithium cells. Yet, the lithium cells may be damaged and the service life thereof may be shortened in the absence of reliable approaches for the switching operation. In addition, the actual switching during charging cycles may be associated with a corresponding energy loss operation. This may result from electrical (voltage, current, etc.) spikes arising in or from the switching operations to further shorten the service life of the lithium cells.
Another conventional battery charging pattern utilizes a number of charging/discharging cycles to downwardly adjust the charge-off voltage. However, if the lithium cells are charged before their battery's charges are exhausted or discharged before being fully charged this type of conventional approach may not achieve the intended or desired goal of downwardly adjusting the charge-off voltage.
In short, the generally available conventional battery-charging methods generally adjust the battery charging depending on the status of the battery cells without considering other characteristics of the battery cells.